High-pressure mercury vapor halogen lamp having an electrode thermally insulated from lead-in conductor



INVENTORJ .C.DRIESSEN AGENT CORNELIS AJJACOBS ANTONIUS J G 3 u :v AU 1 5 l ./7. p 1 1 u I A r; v v ,1 1 I 06L 1967 c. A. J. JACOBS ETAL HIGH-PRESSURE MERCURY VAPOR HALOGEN LAMP HAVING AN ELECTRODE I THERMALLY INSULATED FROM LEAD-IN CONDUCTOR Filed Sept. 27. 1965 v United States Patent Ofilice ABSTRACT OF THE DISCLOSURE A high-pressure mercury vapor halide lamp employing an electrode having an outer part connected to a current supply wire and an emitter body positioned Within the outer part and heated by the discharge. The emitter body is positioned within the outer part in poor heat transfer relationship to the outer part and fills at least half of the space within the outer part so that it retains the heat produced by the discharge and no halide layer which would increase ignition voltage is formed thereon.

The invention relates to 'a high-pressure vapor discharge lamp which contains mercury and a halogen. The invention further relates to an electrode for such a lamp.

A high-pressure vapor discharge lamp is to be understood to mean a lamp in which, during operation, the discharge is contracted and the pressure does not exceed approximately 50 atm.

High-pressure vapor discharge lamps have been known for some time already. They are frequently used in those cases in which a very high luminous efficiency and a high eficiency of light conversion of the number of watts supplied to the lamp into useful lumens is desired. The drawback of lamps of this type, which contains mercury vapor only and sometimes a rare gas to facilitate the ignition, is that the color of the emitted radiation is not very suitable for a natural color reproduction. Means to improve these color reproductions are, for example, the use of luminescent layers and the use of filters. This latter means has the drawback that the luminous efiiciency is reduced. Recent publications described another means to improve the color reproduction which does not adversely influence the luminous etficiency and the efiiciency and sometimes even improves these efiiciencies. For that purpose, the discharge space is filled with certain elements, for example, sodium, indium, thallium, tin or lithium, which add certain colors to the spectrum which is emitted by the lamp, in addition to the mercury vapor and the rare gas which is possibly present. Since the vapor pressure of the said elements at the commonly used temperatures in the discharge space usually is not sufficient, the elements are usually introduced into the discharge space as halides. For that purpose are used in particular the iodides of the said elements, in addition, often a quantity of additional halogen, for example iodine, is provided in the discharge space. During the use of such lamps a cycle occurs, in which the halides decompose at places With high temperatures and recombine again at places with low temperatures.

Lamps of the above type, both with and without halogens comprise at least two electrodes which usually are heated only by the discharge itself. These electrodes are connected to a current supply wire, which is passed out of the discharge space, for example, through a so-called pinch. When the lamps are switched off, the electrodes cool rather rapidly partly as a result of radiation and 3,349,276 Patented Get. 24, 1967 partly as a result of dissipation of heat through the current supply Wires and the pinch. The result is that during the cooling period the electrodes assume a lower temperature than other parts of the lamp, for exa1nple, the wall of the discharge space. As a result of this the halides will recombine on the surface of the electrode; in consequence of this, the electrodes are coated with a layer of the halides.

Most electrodes for this type of lamps contain an uncoated metal part, for example, tungsten, and a part which consists of emitting material arranged on a metal carrier, for example, tungsten. When the lamps are switched on, the discharge begins on the part.which contains emitting material, for example, thorium oxide and, when the whole electrode has reached a given temperature, proceeds to the part which is not coated with emitting material.

During the above-mentioned cooling period after switching off the known lamps, both the non-emitting and the emitting parts of the electrode is covered with a layer of halide. In particular the coating on the emitting part is very disturbing because, when the lamps are switched on again, the ignition voltage proves to be considerably higher than at the instant when the lamps were switched on for the first time.

It is the object of the invention to provide an improved construction of the electrodes.

A high-pressure mercury vapor halogen discharge lamp according to the invention is characterized in that in the discharge space there is at least one electrode which is connected to a current supply wire and is heated by the discharge itself. This electrode comprises an outer metal part which is in electrical and heat-conducting relationship with the current supply wire and which envelopes a space which is substantially entirely open at least on the side remote from the current supply wire. An emitter body is arranged within the outer metal part in such manner that it can deliver its heat to the current supply wire with difficulty and occupies at least half of the space inside the outer metal part.

As a result of the arrangement of the emitter body according to the invention, the emitter body during the cooling period is not cooled as rapidly as the remaining part of the electrode. This is obtained partly because the emitter body can transmit its heat to the current supply wire with difficulty and partly because the emitter body occupies at least half of the space in the electrode. This latter requirement is just as necessary as the former, because otherwise the emitter body would have too low a thermal capacity and would still cool too rapidly by radiation. In an electrode in a lamp according to the invention, a layer of halogen can be deposited on the nonemitting part of the electrode, it is true, but this has a far smaller influence on the increase of the ignition voltage than a deposit on the emitting part.

The emitter body may consist wholly of emitting material, for example, thorium oxide; however, it consists preferably of a carrier, for example, tungsten metal, with a layer of emitting material provided on it. The thermal capacity of the emitter body is greatly increased by it. In fact, the quantity of emitter required for a satisfactory ignition is so smallthat the weight of the emitter would be too small to obtain a large thermal capacity.

Starting from the above requirements for the construction of the electrodes several embodiments are possible. For example, the outer metal part may consist of a coiled wire, for example, of tungsten. Inside this coil the emitter body is arranged. This emitter body has a poor thermal conductingcontact with the outer coil; as a result of this the heat dissipation to the current supply wire connected to the outer coil is small.

In this embodiment the emitter body preferably consists also of a tungsten coil, the diameter of which must, of course, be smaller than that of the outer coil. This inner coil is previously coated with emitting material or with the material from Which the emitting material can be formed, for example, by a thermal treatment. Both the outer and the inner coil can be closed or open which means that the windings of the coils engage each other or do not engage each other.

On the side remote from the current supply wire, the space inside the outer coil is substantially entirely Open. As a result of this the discharge can start on the emitting body. The outer coil preferably projects somewhat beyond the inner coil in the direction remote from the current supply wire. As a result of this the discharge in the operating condition will no longer act upon the emitter coil but upon the outer coil. The end of the outer coil at this side is preferably bent inwards somewhat after the inner coil has been arranged, as a result of which the inner coil is prevented from falling of the outer coil. The outer coil may be secured to the current supply wire by welding. On the side of the current supply wire the coil is preferably narrowed to such an extent that the last turns thereof exactly fit around the current suppyl wire.

An electrode according to another particularly favorable embodiment consists of an open coil the two ends of which are straight and lie substantially on the axis of the coil in a manner such that one end lies inside the coil and the other end projects beyond the coil. This end is connected to the current supply wire. The emitter end is supported by the end which lies inside the coil. In this case also, the emitter body preferably consists of a coil coated with emitter. The heat dissipation of the emitter body of the current supply wire consequently covers the whole length of the outer coil. As a result of this, when the lamp is switched off, the emitter coil will remain warm longer than the outer coil and no halide layer can be formed on the emitter body.

The invention will now be described with reference to the accompanying drawing, in which FIGURE 1 diagrammatically shows a discharge lamp according to the invention,

FIGURE 2 shows an embodiment of an electrode for a lamp of FIGURE 1, and

FIGURE 3 shows another advantageous embodiment of an electrode for a lamp of FIGURE 1.

In FIGURE 1 the tubular gas discharge lamp which is manufactured from a readily heat resisting light-pervious material, for example, quartz glass, is denoted by 1. The two ends of the tube 1 are formed into pinches 2 and 3 respectively. The current supply wires 6 and 7 respectively are secured in these pinches in a vacuum-tight manner. The cathodes 4 and respectively are secured to the current supply wires. An ignition electrode is indicated by 8. Such an ignition electrode is frequently used to introduce the discharge. If required, the lamp may be arranged in an evacuated outer envelope.

In FIGURE 2, which shows a cross-section through an electrode for a discharge lamp of FIGURE 1, the current supply wire is denoted by 10. This current supply wire consists, for example, of tungsten. On the side of the discharge a tungsten coil 11 is secured on the said current supply wire 10. This coil encloses a space 12 in which the emitter body is arranged. This emitter body consists of a tungsten coil 13 on which and in which an emitter 14 has previously been provided.

As is shown in the figure the space inside the coil 11 is substantially entirely occupied by the emitter body 1344. The heat dissipation of this body to the current supply wire 10, must be effected entirely through the coil 11. The loss of heat along this path is rather small since the heat-conducting relationship between the coils 13 and 11 is poor, in particular as a result of the intermediate emitter layer. The mass of the emitter body 13-14 is comparatively large. As a result of this, the loss of heat by radiation will be smaller than if, for example, the space inside the coil were not filled to such an extent with the emitter body, as would he the case, for example, if a thin emitter layer were provided on the inside of the coil 11. In that case, it is true, the heat dissipation through the coil 11 to the current sup ply wire 10 would also be rather small but the emitter would still cool too rapidly by radiation and as a result be coated with a halide layer. The emitter body 13-14 is arranged in a space inside the coil 11 in a somewhat clamped manner. In order to prevent it from falling out, the uppermost turn 15 of the coil is bent inwardly as is shown in the figure.

FIGURE 3 shows a cross section of an embodiment of an electrode for a discharge lamp according to the invention in which the outermost part consists of an open coil 16. One end of the said coil is formed into a straight portion 17 which substantially lies in the axis of the coil 16. This portion 17 is connected to the current supply wire 18. The other end of the coil 16 is formed into a straight portion 19 which also lies substantially in the axis of the coil. The emitter body which consists of a coil 20, for example, of tungsten, which is coated with emitter material 21, is arranged around the said straight portion 19. The heat dissipation of the emitter body 20-21 to the current supply wire 18, also is effected entirely along the coil 16. As a result of this, the emitter body 20-21, after switching off the lamp, will remain warm longer than the coil 16. So it will be difficult for a halide deposit to form on the emitter body 20-21. In fact, the coil 16 is always colder than the emitter body. The mass of the emitter body 20-21 is so large than the heat of the emitter body 20-21 is not lost too rapidly by radiation.

It has been found in experiments with a great number of lamps, according to the invention that the ignition voltage, after the lamps had been switched on and switched oil a number of times, lies from 30 to volts lower than in similar lamps operated under the same conditions which were not provided with electrodes according to the invention.

What is claimed is:

1. In a high-pressure mercury vapor halogen discharge lamp including a light-transmissible envelope enclosing a discharge space containing mercury and a halide, an electrode within said discharge space heated by a discharge and connected to a current supply wire, said electrode comprising an outer metal portion in electrical and heat conducting relationship with said current supply wire, said outer metal portion enclosing a space open on the side remote from the current supply wire,

an emitter body positioned within said outer metal portion in poor thermal transfer relationship to said current supply member and occupying at least half of said space enclosed by said outer metal portion whereby the formation of a halide layer on said emitter body is inhibited.

2. A high-pressure mercury vapor halogen discharge lamp as claimed in claim 1, characterized in which the emitter body is constituted of an electron emissive material and is provided on a metal carrier, the thermal capacity of the carrier exceeding the thermal capacity of the emitting material.

3. A high-pressure mercury vapor halogen discharge lamp as claimed in claim 2, in which the emitter body comprises a metal coil which is coated and at least partially filled with emitting material.

4. A high-pressure mercury vapor halogen discharge lamp as claimed in claim 3, in which the metal coil is tungsten and the emitter material is thorium oxide.

5. A high-pressure mercury vapor halogen discharge lamp as claimed in claim 4 in which the outer part of the electrode is a metal coil which is in poor heat-conducting relationship with the emitter body.

6. A high-pressure mercury vapor halogen discharge lamp as claimed in claim 5, in which the end of the outer coil remote from the current supply wire is bent inwardly.

7. A high-pressure mercury vapor halogen discharge lamp as claimed in claim 5 in which the outer end of the electrode is an open metal coil, two ends of which are straight and lie substantially on the axis of the coil one end lying inside the coil and the other end projects beyond the coil and being connected to the current supply wire, and the emitter body being supported by the end which lies inside the coil.

6 References Cited UNITED STATES PATENTS 2,177,703 10/ 1939 Francis 313-3461 3,029,359 4/1962 White 313346 X 3,170,081 2/1965 Rokosz 313213 3,195,005 7/1965 Freeman 313-217 FOREIGN PATENTS 107,110 4/ 1939 Australia. 943,535 12/ 1963 Great Britain.

S. D. SCHLOSSER, Primary Examiner. 

1. IN A HIGH-PRESSURE MERCURY VAPOR HALOGEN DISCHARGED LAMP INCLUDING A LIGHT-TRANSMISSIBLE ENVELOPE ENCLOSING A DISCHARGE SPACE CONTAINING MERCURY AND A HALIDE, AN ELECTRODE WITHIN SAID DISCHARGE SPACE HEATED BY A DISCHARGE AND CONNECTED TO A CURRENT SUPPLY WIRE, SAID ELECTRODE COMPRISING AN OUTER METAL PORTION IN ELECTRICAL AND HEAT CONDUCTING RELATIONSHIP WITH SAID CURRENT SUPPLY WIRE, SAID OUTER METAL PORTION ENCLOSING A SPACE OPEN ON THE SIDE REMOTE FROM THE CURRENT SUPPLY WIRE, AN EMITTER BODY POSITIONED WITHIN SAID OUTER METAL PORTION IN POOR THERMAL TRANSFER RELATIONSHIP TO SAID CURRENT SUPPLY MEMBER AND OCCUPYING AT LEAST HALF OF SAID SPACE ENCLOSED BY SAID OUTER METAL PORTION WHEREBY THE FORMATION OF A HALIDE LAYER OF SAID EMITTER BODY IS INHIBITED. 